Many contemporary devices have been developed to rely not only on earth-orbiting satellites for navigation purposes, but also ground-based stations for inter-device communication. Specialized products have been created to address communication between a flying object and both earth-based stations and earth-orbiting satellites.
Contemporary antennas used on flying equipment typically have a blade design, such that the antenna protrudes off the surface of the equipment with the edge of the blade design facing the direction of travel. This sort of design gives rise to high drag when the equipment is in use, as the protrusion affects the aerodynamic nature of the equipment. Also, this sort of design can cause physical interference with other devices on the flying equipment, as the antenna is an external device placed on the equipment's outer hull. In situations where these antennas are initially housed within the body of the flying equipment, to be later deployed for communication purposes, deployment can cause physical interference with other features of the equipment, as pre-deployment space for the antennas cannot be used for other payloads. Also, additional mechanisms are added to effect the deployment of these antennas. Transmission and reception patterns of such blade antennas have similar gain in axial and transverse directions.
Patch antennas have also been used in flying equipment. Using such antennas has significant effects on the directionality of potential communication. Patch antennas are thin antennas printed close to a ground layer, and occasionally attached to the hull of the flying equipment. These antennas often transmit and receive signals in a direction perpendicular to the surface on which they are attached. As a result, these antennas are often unable to provide their greatest gain in both the aft and forward directions, but rather only in a single direction.
Helical antennas have widespread useage in traditional satellite communication systems. This is partly due to the antenna's ability to produce and receive circularly polarized radiation, the type of radiation often used in such systems. Also, because the radiation pattern of such antennas is nearly hemispherical, they are well suited for such communications.
There are applications where transmitting and receiving signals occur at different frequencies. In such circumstances, it is desirable to have a dual-band antenna. However, often the configurations available in conventional dual-band helical antennas are less than desirable. One example is to place two single-band helical antennas end-to-end so that they form a single cylinder. This addresses the need for dual band; however it significantly increases the length of the antenna.
A major use of dual-band functionality is to accommodate separate transmit and receive frequencies. In many applications, such transmit/receive functions ensure that transmissions are complete before a responding signal is sent by a device. However, due to the coupling between the transmitter and receiver, if the antenna were to transmit and receive signals simultaneously significant interference could occur between the signals, degrading the integrity of the communication. If dual-band functionality is obtained from separate antennas, the antennas traditionally are mounted a distance apart and/or incorporate extra filtering to separate and isolate the transmit and receive signals. It is desirable for a dual-band antenna system, consisting of two antennas mounted in close proximity, to have high isolation between the two systems so that interference between the simultaneous transmit and receive signals do not degrade the integrity of the communication. While separate filters can be used to increase this isolation, they are undesirable because of their size, weight, cost and attenuation of the signal.
Also, due to the physical structure of contemporary helical antennas, these devices, when used with flying equipment, would be placed external to the surface, or associated with a deployment mechanism to ensure that the antenna can transmit and receive signals. These are problematic solutions because a permanent fixture upon the surface of a flying object increases the drag of the object, and a deployment mechanism may interfere with other functions of the device.
Flying equipment is generally restricted to small weight and size limitations, as the larger and heavier an object is, the more costly the equipment is. The transmitting and receiving circuitry associated with any antenna must be housed in some unit along with other component circuitry to facilitate communication. The physical structure of contemporary helical antennas requires an external housing separate from the antennas for such circuitry. This increases the weight and complexity of the flying equipment, as proper shielding and housing must be created to ensure that the components are held safely.
In order to ensure that an antenna can function at the requisite frequency, the antenna must be tuned. The process of tuning an antenna becomes more difficult when multiple antennas operating at different frequencies are brought together into a system. Conventionally, in such systems, tuning any one antenna will affect the tuned frequencies of the other antennas in the system. The complexity of the tuning process increases when the antennas are closely positioned together in the system.